Background: Chest radiographs are an easy and relatively inexpensive method for imaging the tissues and structure of the thorax (chest). Chest x-rays are typically taken with two views, a frontal (posterior-anterior or PA), and a lateral view. Additionally, oblique views, angle from either side, are sometimes added to assist the reader. Chest radiographs are a useful tool in diagnosing pneumoconioses or dust diseases of the lungs.
The International Labour Office (“ILO”) is the International Labour Organization’s research body and publishing house. Since 1950, the ILO has periodically published Guidelines on how to classify chest x-rays for pneumoconioses. The most recent edition (2000) of the Guidelines, replaced the 1980 revised edition. The ILO Classification helps describe and record x-ray abnormalities of pneumoconioses in a simple, systematic, and reproducible manner, for epidemiological studies, screening and surveillance, clinical purposes, medical research, and aiding international comparisons of data.
“B” Reader Program: In 1974, after studies of surveillance programs for coal miners revealed unacceptable degrees of variation amongst x-ray readers, the National Institute for Occupational Safety and Health (NIOSH), in conjunction with the ILO, began the “B” reader program (so named because of the Black lung or Coal Workers’ X-ray Surveillance Program), with the intent to train and certify physicians in the ILO Classification system. The “B” reader certification examinationwent into full operation in 1978. NIOSH “B” reader approval is granted to physicians with a valid medical license who demonstrate proficiency in the classification of chest radiographs for the pneumoconioses using the ILO classification system. After passing the B-reader proficiency examination, a B-reader qualification by NIOSH designates physicians as competent in classifying pneumoconiosis films. I am a NIOSH-certified “B” reader, and have been so since 2003.
ILO Classification: The ILO Classification allows for systematic recording of the radiographic findings for all types of pneumoconioses. The Classification is designed for reporting the findings on a posterior-anterior view of the chest, but this does not exclude the use of other views in the clinical assessment of the patient. The x-ray should be analog-type (not digital) and of standard size (no less than 14 x 17″).
The ILO Classification system includes printed Guidelines and standard x-rays. The reader compares the subject chest x-ray with those of the standard set. The standard films provide differing types (“shape and size”) and severity (“profusion”) of abnormalities seen in persons with pneumoconiosis, including asbestosis, silicosis, and coal-workers’ pneumoconiosis. The reader then classifies the subject film, often recording the findings on the NIOSH Roentgenographic Interpretation form (sometimes referred to as the ILO form). The ILO Classification system pertains to pulmonary parenchymal (tissue) abnormalities (small and large opacities), pleural changes (pleural plaques, calcification, and diffuse pleural thickening) and other features associated, or sometimes confused, with occupational lung disease.
Quality of x-ray: Even when an obvious radiographic abnormality is present, it is necessary to review the chest x-ray in a systematic fashion. The ILO evaluation begins with an assessment of the x-ray quality. There are four grades of radiographic quality in the ILO system. Quality 1 is a good quality film, quality 2 and 3 are acceptable but with some technical defect, and quality 4 is unacceptable for ILO classification. The degree and location of film quality defects or artifacts determines the overall quality rating. Technical defects should be taken into consideration by the reader. A common quality defect, under-exposure, results in a tendency to read more profusion than would be recognized on an optimally produced radiograph. In other words, a reader is more likely to see mildly increased interstitial changes even though they are not present. Conversely, over-exposure produces the opposite affect.
Small parenchymal abnormalities: After assessing the x-ray quality, the B-reader evaluates the x-ray for the presence of any small parenchymal opacities consistent with pneumoconiosis. He or she will compare the subject PA radiograph with the ILO standard films to arrive at the profusion, shape/size, and location of small opacities.
- Profusion: Profusion refers to the concentration of small opacities in the affected zones of the lung. Using the Standard x-rays, the profusion (concentration) of small opacities is classified on a 4-point major category scale (0, 1, 2, or 3), with each major category divided into three, giving 12 ordered subcategories of increasing profusion: 0/-, 0/0, 0/1, 1/0, 1/1, 1/2, 2/1, 2/2, 2/3, 3/2, 3/3, and 3/+. Category 0 refers to the absence of small opacity and category 3 represents the most profuse. The major category (first number) represents the profusion felt to best fit the subject film, and the minor category (second number) represents the profusion seriously considered as an alternative. According to the American Thoracic Society (ATS), profusion 0/1 and 1/0 is the dividing point generally taken to separate films that are considered “negative” from those that are considered to be “positive.”
- Shape/size: The small parenchymal opacities are either rounded or irregular (linear). The small, rounded opacities are “p” (up to about 1.5 mm), “q” (about 1.5 mm to about 3 mm), or “r” (exceeding about 3mm and up to about 10 mm). Small, irregular opacities are classified by width as “s“, “t”, or “u” (same respective sizes as for small, rounded opacities.
- Location: Each lung is mentally subdivided by the reader into 3 evenly spaced zones: upper, middle, and lower. The zones in which the small parenchymal opacities appear are recorded.
Large opacities: A large opacity is defined as any opacity greater than 1 cm in diameter. They are classified as Category A (for one or more large opacities whose combined longest dimension does not exceed about 50 mm), Category B (for one or more large opacities whose combined longest dimension exceeds 50 mm but does not exceed the equivalent area of the right upper lung zone), or Category C (for one or more large opacities whose combined longest dimension exceed the equivalent area of the right upper lung zone).
Pleural abnormalities: Pleural abnormalities are reported with respect to type (pleural plaques or diffuse pleural thickening), location (chest wall, diaphragm, or other), presence of calcification, width (only of in profile pleural thickening seen along the chest wall edge), and extent (combined distance for involved chest wall).
Other abnormalities: There are 29 “obligatory” symbols representing important features related to dust diseases of the lungs and other etiologies. These symbols are: aa atherosclerotic aorta; at significant apical pleural thickening; ax coalescence of small opacities; bu bulla(e); ca cancer; cg calcified granuloma or lymph node; cn calcification of small pneumoconiotic opacities; co abnormal cardiac shape or size; cp cor pulmonale; cv cavity; di marked distortion of an intrathoracic structure; ef pleural effusion; em emphysema; es eggshell calcification; fr rib fractures; hi enlargement of non-calcified hilar nodes; ho honeycombing; id ill-defined diaphragm border; ih ill-defined heart border; kl septal (Kerley) lines; me mesothelioma; pa plate atelectasis; pb parenchymal bands; pi pleural thickening of an interlobar fissure; px pneumothorax; ra rounded atelectasis; rp rheumatoid pneumoconiosis; tb tuberculosis; and od other disease or significant abnormality. Finally, the reader comments on any other abnormal features of the chest radiograph or other relevant information.